The present invention relates to a traffic control system, and in particular relates to an on site pre-timed unit which can be utilized as a back-up unit to centrally controlled traffic control systems or as an inexpensive stand alone unit in areas which cannot easily be controlled by a central system.
Originally traffic control systems were of an electromechanical nature. A motor would rotate a number of cams connected to its shaft. The cams activated contact switches which in turn controlled the traffic lights. These systems suffered from limited reliability, were relatively expensive to manufacture and to maintain, and the timing could only be changed by exchanging the cam set.
Present day stand alone units are mostly digital in nature, and are often programmable through the use of dedicated software. These units are rather expensive to manufacture, are complex and thus prone to failure and require highly skilled maintenance. Moreover, in case of a power failure, they become non-operational.
More sophisticated systems rely on a central master controller which is programmed to control a number of slave units located at the various intersections. These systems are capable of varying the operational timing at the controlled intersections in response to changes in traffic conditions, traffic patterns during the day, weather conditions and other relevant factors. Although highly sophisticated, they become non-operational in the case of power failure or a failure of the master or slave units.
The present invention is designed to be utilized as a back-up unit to either stand alone systems or to master-slave installations and be made operational either in case of failure of the main unit or of the power source.
The traffic controller in the present invention reduces complexity and cost by relying, for the generation of the timing sequence for the operation of the lights, on a novel resistance/capacitor timing circuitry which can generate stable and required long time pulses of varying duration to control the traffic lights.
Although portable back-up units are known (Foreman, U.S. Pat. No. 4,008,404, Feb. 15, 1977), these units rely on digital timing circuitry for the generation of the required time intervals. Such circuitry results in relatively complex and costly equipment.
The present unit is also capable of operating with a DC power supply in case of an AC power failure. Although the operation of electronic equipment with alternate power source is well known and is also utilized in traffic controllers (Studer, U.S. Pat. No. 3,629,000, Dec. 21, 1971), the present unit does not utilize the traditional method of converting the DC power into AC through the use of an inverter but includes independent dual driving circuitry for the AC and DC operation of the traffic lights. This results in better energy utilization and longer battery life in the DC operating mode.